The \(n_a\)  field acceleration \(n^b \nabla _b n_a\)  becomes non-trivial in the case. (Indirectly, that means the presence of a non-trivial Hájiček field [1]}, see below.) However, one can still use the standard expression of [2]} for a stretched membrane stress-tensor
\(8\pi G t_{ab}=Kh_{ab}-K_{ab},\qquad h_{ab}=g_{ab}-n_an_b,\) 
